Plate-fin-type heat exchanger

ABSTRACT

A plate-fin-type heat exchanger for transferring heat from a hot fluid to a cold fluid includes stacked plates having fins therebetween that define alternate interdigitated first and second fluid passages, the fins defining the first fluid passages having a high coefficient of heat transfer and a large area of heat transfer and the fins defining the second fluid passages having a low coefficient of heat transfer and a small area of heat transfer. Either the hot fluid or the cold fluid is continuously passed through the first fluid passages and the other fluid is intermittently passed through the second fluid passages.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a plate-fin-type heat exchanger whereina high temperature fluid or a low temperature fluid flows continuouslytherethrough, while the other flows intermittently therethrough, andrelates to a plate-fin-type heat exchanger wherein thermal fatigueproduced particularly in a separating plate partitioning between thepassages through which the high temperature fluid flows and the passagesthrough which the low temperature fluid flows is alleviated.

2. Background Art

The plate-fin-type heat exchanger has a large area of heat transfer perunit area and a high coefficient of heat transfer, and therefore has anadvantage in that it is compact and easily made in comparison with othertypes, particularly tube type heat exchangers.

Also, the plate-fin-type heat exchanger has a wide range of selection ofdesign such that the fin pitch, the fin height and the fin shapesuitable for the nature and the purpose of the fluid flowing througheach passage can be properly selected, and further the number oflaminations of fins can be selected arbitrarily, and thereby anefficient design can be made, so that it has been used for a variety ofapplications.

On the other hand, where such a plate-fin-type heat exchanger is appliedto the case where one of a higher temperature fluid and a lowtemperature fluid performs continuous operation and the other operatesintermittently, the temperature of the separating plate which is apartition plate between the fluid passages is largely varied repeatedly,and therefore thermal fatigue is produced, and a long-time use thereofmight result in damage.

For the plate-fin-type heat exchanger having the above-mentionedconfiguration, the temperature of the separating plate between theadjacent passages during operation is given by the following equation.##EQU1## where, Q: Quantity of heat exchange (Kcal/hr)

hA_(H) : Coefficient of heat transfer x area of heat transfer(Kcal/h°C.) of high temperature side

hA_(L) : Coefficient of heat transfer x area of heat transfer(Kcal/h°C.) of low temperature side.

T_(H) : Temperature of fluid of high temperature side, °C.

T_(L) : Temperature of fluid of low temperature side, °C.

T_(W) : Temperature

Here, consideration is made on the temperature of the separating platein intermittent operation.

When the high temperature side is in normal operation, and the lowtemperature side is in the stopped state,

    T.sub.W =T.sub.H.

When the high temperature side is in normal operation, and the lowtemperature side starts to operate, the temperature T_(W) is reduced,being balanced at a certain temperature.

Taking the temperature of the separating plate when the low temperatureside is inactive as T_(W1) (=T_(H)), and the temperature of the platebalanced after a lapse of some time from start of operation of the lowtemperature side as T_(W2), the temperature of the separating platevaries repeatedly between T_(W1) (=T_(H)) and T_(W2). No problem existsif this variation in temperature takes place slowly and uniformly, butactually, this variation occurs in a nonuniform fashion, causinggeneration of thermal stress.

Next, taking the amount of change in the temperature as (T_(W1)-T_(W2))=ΔT_(W), thermal stress is expressed by the following generalequation.

    σ=ExaxΔT.sub.W

E: Young's modulus

a: Coefficient of thermal expansion of separating plate,/°C.

ΔTW: (T_(W1) -T_(W2))

As shown by the above equation, as the amount ΔT becomes smaller, thethermal stress becomes smaller and the life or durability is increased.

However, for the plate-fin-type heat exchanger wherein either of thehigh temperature fluid and the low temperature fluid passes throughintermittently, no heat exchanger has been proposed which has aconfiguration that the variation in the temperature of the separatingplate between the passages is positively minimized, and conventionallymaterials being resistant to thermal stress have been selected.

The present invention proposes to provide a plate-fin-type heatexchanger wherein the thermal fatigue is alleviated which is produced inthe separating plate partitioning between the high temperature passageand the low temperature passage of the plate-fin-type heat exchangerwherein one of the high temperature fluid and the low temperature fluidis operated continuously, while the other repeats intermittentoperation, and thereby the life of the heat exchanger is extended.

SUMMARY OF THE INVENTION

In the present invention, in a heat exchanger wherein one of a hightemperature fluid and a low temperature fluid performs continuousoperation, while the other repeats intermittent operation, aplate-fin-type heat exchanger having a configuration capable ofalleviating thermal fatigue produced in a separating plate partitioningbetween a passage of high temperature side and a passage of lowtemperature side is aimed and various studies have been conducted, andas a result, considering that a corrugated fin which is the feature ofthe plate-fin-type heat exchanger can be selected arbitrarily, the ratioof hAs (coefficient of heat transfer x area of heat transfer) of thepassages is increased, and thereby the amount of variation in thetemperature of the separating plate repeated intermittently can bedecreased, and it has been found that a reduction in life due to thermalfatigue can be improved.

This means that the present invention is:

In a plate-fin-type heat exchanger wherein one of a fluid of hightemperature side and a fluid of low temperature side performs continuousoperation, while the other repeats intermittent operation,

a plate-fin-type heat exchanger characterized in that passages of thefluid of continuous operation side are disposed outside, and dummypassages passing no fluid are disposed in a laminated fashion on theoutermost side, and

fins having a high coefficient of heat transfer and a large area of heattransfer are used for a fluid passage of continuous operation side, andfins having a low coefficient of heat transfer and a small area of heattransfer are used for a fluid passage of intermittent operation side.

Further detailed description is made on the present invention.

Where the continuous operation side is a passage of heat medium as shownin the embodiment, the plate-fin-type heat exchanger is configurated ina manner that the passages of high temperature side of a configurationthat a corrugated fin is incorporated between two plates and the bothends are closed with side bars and the passages of low temperature sideof nearly the same construction are laminated alternately, and the dummypassages which have nearly the same construction as each passage andpass no fluid are laminated outside the both end passages respectively,and further

(1) the fin having a high coefficient of heat transfer and a large areaof heat transfer is used for the passage wherethrough the heat mediumpasses continuously during operation, and the fin having a lowcoefficient of heat transfer and a small area of heat transfer is usedfor the passage wherethrough the heat medium passes intermittently in acertain time cycle during operation, and the ratio of hAs (coefficientof heat transfer x area of heat transfer) is increased,

(2) the passage continuously passing the heat medium is disposed outsidethe passage of intermittent side, and

(3) the number of the dummy passages of the outermost side of the heatexchanger core are set to two or more. Or, further,

(4) it is desirable to use the corrugated fin of the lower half of theinlet side of the heat exchanging part in the passage of intermittentpart having a coefficient of heat transfer and an area of heat transferequivalent to those of the corrugated fin of the fluid distributingpart.

In the present invention, for the fin having a high coefficient of heattransfer and a large area of heat transfer, a corrugated fin having alarge number of corrugations can be used, and for the fin having a lowcoefficient of heat transfer and a small area of heat transfer, acorrugated fin having a small number of corrugations can be used, andthe corrugated fins of different numbers of corrugations can be used incombination in the same passage, and further, different fin materialscan be used in combination as required.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustrative view showing an A passage of a plate-fin-typeheat exchanger in accordance with the present invention.

FIG. 2 is an illustrative view showing a B passage of the same.

FIG. 3 is a perspective illustrative view showing the plate-fin-typeheat exchanger in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Description is made of a plate-fin-type heat exchanger wherein air isused for a fluid of high temperature performing continuous operation,and a cold gas is used for a fluid of low temperature performingintermittent operation.

The plate-fin-type heat exchanger of the present invention is configuredin a manner that a large number of passages wherein a requiredcorrugated fin is sandwiched between separate fins and is closed withside bars are laminated, and air passages of high temperature side (Apassage), cold gas passages of low temperature side (B passage) anddummy passages (D passage) allowing no fluid to pass through arelaminated in a 59-state-arranged manner as shown below.

D₁, D₂, A₃, B₄, A₅, B₆ . . . B₅₄, A₅₅, B₅₆, A₅₇, D₅₈, D₅₉ (Note that thesequence of arrangement and the number of stages are shown from theoutside of one toward the outside of the other.)

The A passage has a configuration for passing air downward from above,and as shown in FIG. 1, the fin edge lines are lined up vertically andthe number of edge lines per unit length (18 fins/inch) is large, thatis, the corrugated fin having a large area of heat transfer and a highcoefficient of heat transfer (1) is used.

The B passage has a configuration for passing a cold gas upward frombelow, and as shown in FIG. 2, the number of edge lines per unit length(12 fins/inch) is large in the center part (the corrugated fin edgelines are lined up vertically) and the outlet part (two-triangulardistributing part) except for the inlet part. This means that thecorrugated fin of low coefficient of heat transfer (3) having aperformance of about two-thirds of the coefficient of heat transfer ofthe A passage is used, and further in the inlet part, that is,two-triangular distributing part in the drawing, the corrugated finhaving a low coefficient of heat transfer (2) is used which has a numberof edge lines per unit length (6 fins/inch) which is one-third of thenumber of edge lines per unit length of the corrugated fin of the Apassage, that is, has a small area of heat transfer.

On the other hand, for the plate-fin-type heat exchanger to be compared,the above-mentioned corrugated fin having a high coefficient of heattransfer (18 fins/inch) is used for both the A passage and the Bpassage, and only one stage of the D passage is provided, and aplurality of stages are laminated in the sequence of arrangement of D,B, A, B, A . . . A, B, A, B, D.

The above-mentioned plate-fin-type heat exchangers are operated underthe same conditions in a manner such that a cold gas is introducedintermittently into the B passages and heat exchange is performed, andthe temperature of the cold gas inlet side at the separating platebetween the A passage and the B passage of the outermost side wasmeasured. Then, in the heat exchanger to be compared, the temperaturedifference was 30°-50° between the case of introducing the cold gas andthe case of introducing no gas, but in the case of the heat exchanger inaccordance with the present invention, the difference is reduced toabout 15° C., and generation of thermal stress can be reduced, and it isunderstandable that the life of the heater exchanger can be extended.

The present invention is optimum for the plate-fin-type heat exchangerwherein one of a fluid of high temperature and a fluid of lowtemperature performs continuous operation and the other repeatsintermittent operation such as the heat exchanger which, to heat a fluidof low temperature, performs heat exchange by periodically passing thefluid of low temperature through the heat exchanger wherethrough a fluidof high temperature flows all the time, or in reverse, the heatexchanger which, to cool a fluid of high temperature, performs heatexchange by periodically passing the fluid of high temperature throughthe heat exchanger wherethrough a fluid of low temperature flows all thetime.

For example, when the present invention is applied to the preheater forreproducing molecular sieves having a configuration that cool waste gasflows periodically into the heat exchanger the whole of which has becomethe air temperature and heat exchange is repeated intermittently,generation of thermal stress due to the temperature difference can bereduced, and the extended life of the heat exchanger can be achieved,and thereby the best effect can be expected.

We claim:
 1. A plate-fin-type heat exchanger for transferring heat froma hot fluid to a cold fluid, said heat exchanger defining opposite firstand second sides, opposite third and fourth sides and opposite first andsecond ends, said heat exchanger including a plurality of parallelplates which are stacked between said first and second sides and whichincludes fins that define alternate interdigitated first and secondfluid passages, said fins defining said first fluid passages having ahigh coefficient of heat transfer and a large area of heat transfer,said first fluid passages being intended to continuously convey a firstof said hot and cold fluids, and said fins defining said second fluidpassages having a low coefficient of heat transfer and a small area ofheat transfer, said second fluid passages being intended tointermittently convey a second of said hot and cold fluids.
 2. A heatexchanger as defined in claim 1, wherein said first fluid passages arestraight and have inlets at said first end and outlets at said secondend, and said second fluid passages have inlets at said third side andoutlets at said fourth side.
 3. A heat exchanger as defined in claim 2,wherein, starting from said third side, said second fluid passages havea first portion which extend towards said fourth side, second and thirdportions which extend in parallel with said first passages and a fourthportion which extends to said fourth side.
 4. A heat exchanger asdefined in claim 3, wherein said third portion of said second fluidpassage includes more fins than said first or second portions.